1. Field of the Invention
The present invention relates to an ATM-network-based connectionless communication system which accommodates local connectionless information, such as data in a local area network (LAN), i.e., information sent by a system arranged to immediately transfer data with the address of a receiving terminal placed in the header of a message without establishing a path to the receiving terminal, in an asynchronous transfer mode (ATM) network that uses a connection-oriented communication system, i.e., a system which, before data transfer is made, verifies that a path to a receiving terminal has been established, and interconnects LANs.
2. Description of the Related Art
Local area networks (LANs) installed in companies, which are progressing in a direction that increases speed and capacity, have been made increasingly large in scale and area. The need for connection among LANs scattered through companies is increasing. In general, LANs are adapted for connectionless communication. In contrast with the connectionless communication system, there is a connection-oriented communication system that is used in a broadband ISDN (integrated services digital network).
The connection-oriented communication system is a system which verifies that a path has been established between sending and receiving terminals before data transfer is made. In contrast, the connectionless (CL) communication system, which is used with LANs, is a system in which data transfer is made immediately with a destination address placed in the header without establishing a path to a receiving terminal.
For connection between networks, for example, local area networks, the so-called Nxe2x88x921 connection is generally established between entities, which is realized through the function of a low layer.
In the case where a large quantity of information is to be transmitted as in file transfer, the time required to establish connection can be disregarded. In the case of transmission of a slight quantity of data, such as addresses, however, if connection were established as in the case of transmission of a large quantity of data, the time therefore could not be disregarded. In the recent LAN/distributed processing systems, such short messages are continually transferred. To meet such a requirement, an idea of dividing connection services into conventional connection-oriented services and connectionless services has been introduced.
The need for accommodating local connectionless information, such as LAN data, by a global connection-oriented type ATM network to establish the connection between LANs is increasing. As a network for establishing the connection between LANs, the MAN (Metropolitan Area Network) is investigated at present, but it is not yet put to practice use. The ATM network is globally recognized as a next generation of broadband ISDN. Thus, building the ATM network in such a configuration as involves the functions of the MAN is very significant.
In general, connectionless information is variable in length and starts with a destination address. In order to accommodate such connectionless information in an ATM network which exchanges information as fixed-length cells, it is necessary to perform cell assembly/disassembly of variable-length data, and destination analysis and routing control on a cell-by-cell basis. In the case of communication of such connectionless information, the upper protocol is provided with a timer having a time-out period of several tens of milliseconds to several hundreds of milliseconds to verify the arrival of information. Although connectionless information was transmitted, if no acknowledgment signal is received from a receiving station until timer runout occurs, then the information will be retransmitted over and over again. Therefore, the cell-by-cell routing analysis must be performed fast, within tens of milliseconds. With the present-day techniques, it is required to perform the routing by means of hardware.
Heretofore, when messages are transferred between pieces of user equipment (UE) such as geographically scattered local area networks (LANs), host computers, etc., a connection unit to which one or more pieces of user equipment are connected terminates geographical or logical interface with the user equipment. Within a relay network, messages are relayed through private lines and packet networks.
FIG. 1 illustrates a prior art message transferring system in a wide-area relay network. In this figure, two or more pieces of user equipment (UE) 2 are connected to a relay network (NW) 1, which comprises UE accommodators 3 for accommodating the respective individual user equipment 2 and packet exchange switches or line exchange switches (SW) 4 for exchanging data within the relay network. Each of the UE accommodators 3 serves as a connection unit.
In FIG. 1, the relay network 1 is a packet switched network or line switched network. On this communication network, permanently or semipermanently fixed communication paths are established for message transfers.
With the prior art system of FIG. 1, even if messages are transferred between LANS, the connection between the LANs is not made in such a form as involves the functions of the LANs themselves. Thus, a problem with the prior art is that no ATM network is provided in a form that includes the LAN""s functions.
FIG. 2 is a schematic illustration of a communication system in a local area network. In this figure, a sending terminal 7 places a machine (MAC) address in data to be transmitted and then transmits that data onto a network 8, while a receiving terminal 9 verifies the MAC address, i.e. 133.160.41.99, and then accepts that data from the network 8.
FIG. 3 is a diagram for use in explanation of a prior art inter-LAN communication system using call setting as a communication system which sends LAN communication data as described in connection with FIG. 2 to another LAN over an ATM (asynchronous transfer mode) network. In this figure, data from a sending terminal 11 is sent to a sending-area terminal adapter (TA) 13 via a sending-area LAN 12. In the TA 13, a MAC address is translated into the telephone number of a receiving terminal. A request to call the telephone number is sent to a receiving-area TA 16 via a sending-area ATM switching unit 14 and a receiving-area ATM switching unit 15.
On the other hand, the receiving-area TA 16 alerts the sending-area TA 13 to the completion of the call setting via the ATM switching units 15 and 14. Subsequently, the sending-area TA 13 sends data to be actually transmitted to the receiving-area TA 16. That data is transferred to the receiving terminal 18 via a receiving-area LAN 17. A problem with the prior art communication system utilizing call setting is that data to be transmitted cannot be transferred until call setting is completed between the sending-area TA 13 and the receiving-area TA 16.
In practice, data are transferred as accommodated in fixed-length ATM cells in communicating variable-length connectionless information, such as LAN data, between LANs via an ATM network. In such a case, it will be required to install between the receiving-area ATM switching unit 15 and the TA 16 of FIG. 3 a cell error processing system for detecting errors of received cell.
FIG. 4 is a conceptual diagram of a conventional ATM cell error processing system. A number of n of error processing units 20 are connected in series, where n is the number of types of cell errors. The error processing units 20 exist independently of one another and perform the processes of detecting cell errors, rejecting erroneous cells, and alerting of error information, etc. A failure monitor 19 is alerted by the error processing units 20 of their respective results of error processing.
FIG. 5 is a block diagram illustrating a specific arrangement of the error processing units 20. This circuit arrangement operates as follows.
{circle around (1)} An error checker 21 checks cell data inputs for the presence of cell errors.
{circle around (2)} A cell queuing buffer 22 delays cell data during the process {circle around (1)}.
{circle around (3)} After checking cell errors, the error checker 21 presents a cell reject signal to an erroneous cell rejecting section 23 in the presence of cell errors.
{circle around (4)} The erroneous cell rejecting section 23 is responsive to the cell reject signal to reject a corresponding cell that is in error.
{circle around (5)} The error checker 21 alerts the failure monitor 19 of the result of the error checking.
With the conventional error processing system shown in FIGS. 4 and 5, however, since each of the error processing units 20 performs the processes of detecting cell errors and rejecting cells in error, each error processing unit needs the queuing buffer 22 for detecting cell errors. This results in an increase in the amount of hardware required and the amount of delay introduced in cell data.
Further, in the prior art, after the cell-by-cell error processing, the receiving-area terminal adapter 16 restores the LAN data, i.e., messages and then performs error processing on the messages level, such as address screening error, using addresses placed in message headers and message-length indication, for example. This requires a lot of buffers arranged in message units for disassembly of ATM cells to messages.
It is, accordingly, a first object of the present invention to route variable-length connectionless information, such as LAN information, through a connection-oriented ATM network in a form of fixed-length cells efficiently, at high speed, thereby realizing the connection between LANs.
It is a second object of the present invention to solve various problems encountered in achieving the first object, i.e., in realizing the connection between LANs through the ATM network. One of the problems is simultaneous transmission of the same information from a certain LAN to two or more other LANs. In this case, it is the second object to accommodate connectionless information in the ATM network and transfer the information not only to a single destination but also to two or more destinations designated by, for example, a group address at high speed, efficiently.
It is a third object of the present invention to perform the detection of cell errors in the ATM network and processes associated with the cell error detection efficiently, thereby reducing delays involved in detecting errors and to detect errors on the messages level in the cell stage, thereby eliminating the need for disassembly buffers for detecting message errors.
FIG. 6 is a basic block diagram of the first, second and fifth inventions. More specifically, this figure is a basic block diagram of an ATM-network-based connectionless communication system which accommodates local connectionless information, such as local area network (LAN) data, in a connection-oriented ATM network to realize the connection between LANs.
In FIG. 6, connectionless information cell assembly (cell segmentation)/disassembly means 30 performs bi-directional conversion between variable-length connectionless information, such as LAN data, and fixed-length cells used in an ATM network. The LAN data is converted to fixed-length connectionless cells.
Routing control means 31a (31b, 31c in the second and fifth inventions), which is installed in a switching unit in the ATM network, analyzes the destination address of connectionless information in a connectionless cell obtained by converting LAN data and controls the routing of that cell in the ATM network. The means 31a may be a server.
The ATM network 32a (35b in the fifth invention) is a network that transfers fixed-length cells in an asynchronous transfer mode. In the ATM network, the connectionless information cell assembly/disassembly means 30 and the routing control means 31a are connected by a fixed path, for example, a permanent virtual channel, while the routing control means 31a are connected to each other by a permanent virtual channel serving as a fixed path or by a semi-fixed path, for example, a virtual channel. Note that although, in FIG. 6, each communication path is shown having an arrow pointing in one direction for the sake of convenience, they are all bi-directional.
In FIG. 6, a between-LAN-data-and-cell conversion section constituting the connectionless information cell assembly/disassembly means 30 divides a piece of connectionless information, for example, a message (LAN data) into two or more cells and then places the same message identifier MID in those cells. As segment types, a BOM (beginning of message) is placed in the first cell of the cells resulting from segmentation of that message, an EOM (end of message) is placed in the last cell, and a COM (continuation of message) is placed in any intermediate cell. When a message is converted to a single cell, an SSM (single segment message) is placed in that cell.
Next, a routing information retrieval section in the server, which constitutes the routing control means 31a and performs routing of connectionless cells, retrieves routing information on a route within the ATM network from the destination address of connectionless information contained in the cell in which the BOM or the SSM has been placed.
Subsequently, a MID/routing information temporary storage section in the server temporarily stores the retrieved routing information and the message identifier MID for the cell in which the BOM or the SSM has been placed and retrieves routing information for a cell or cells in which the COM or the EOM has been placed by its or their MID.
Further, a routing information rewriting section in the server rewrites routing information placed in incoming cells by using routing information retrieved for the cells, whereby routing of cells is performed. When the cell having the EOM or SSM is input, an MID erasing section in the server erases the contents of the MID/routing information temporary storage section, thereby terminating the routing for one message.
As described above, according to the first invention, one message, which is connectionless information, is divided into two or more cells, and routing information for the first cell is retrieved by using the addressed destination of that message contained in the first cell. For the intermediate cells and the last cell, the same routing information is retrieved by the message identifier. Thus, the routing of that message is performed.
The second invention is the same in basic block diagram as the first invention. In the second invention, however, when connectionless information with a group address assigned to two or more destinations is sent out to the ATM network, that information is copied, thereby realizing the group addressing facility for forwarding that information to a group of LANs.
The connectionless information cell assembly/disassembly means 30 and the ATM network 32a in the second invention are identical in operation to those in the first invention. The routing control means 31b may also be a server as in the first invention and controls the routing of connectionless cells. When the destination address of connectionless information indicates two or more destinations, the routing control means 31b controls the routing of cells in the ATM network 32a after copying as many cells as needed.
As in the first invention, one message, which is connectionless information, is usually divided into two or more cells, and the same message identifier MID is placed in these cells. For the intermediate and last cells for that message, the message identifier is used to retrieve the same routing information as that for the first cell, thereby routing the cells.
FIG. 7 is a basic block diagram of a third invention. In this figure, the operation of connectionless information cell assembly/disassembly means 30 is the same as in the first invention.
Routing control means 33 analyzes the destination address of connectionless information to control the routing of connectionless cells. In the case of connectionless information having a single destination address, or one-to-one communication, the operation of the control means 33 is the same as that of the routing control means 31a of FIG. 5 illustrating the principle of the first invention. In the case of connectionless information having a group address, or one-to-N (xe2x89xa72) communication, however, the routing control means 33 transfers connectionless cells to message copying means 34, which will be described later, via an ATM network 35 without copying the cells.
The message copying means 34 copies the connectionless cells having the group address from the routing control means 33 by the number of destinations indicated by the group address and controls the routing of the cells to the destinations. That is, such connectionless cells are routed to the destinations by the message copying means 34 through the routing control means 33.
The ATM network 35 makes connection between the connectionless information cell assembly/disassembly means 30 and the routing control means 33 by, for example, a permanent virtual channel, connection between the routing control means 33 and the message copying means 34 and connection between the two routing control means 33 by, for example, a virtual channel serving as a semi-fixed path.
In FIG. 7 illustrating the principle of the third invention, the routing for connectionless cells bound for a single destination is performed between the routing control means 33 as in the first invention. For connectionless cells bound for two or more destinations, on the other hand, the cells are transferred from the routing control means 33 to the message copying means 34, as many cells as needed are copied by the message copying means 34, and the cells are transferred to their respective destinations via the routing control means 33.
FIG. 8 is a basic block diagram of a fourth invention. In this figure, the connectionless information cell assembly/disassembly means 30 is the same in operation as that in the first invention.
Each routing control means 36 is connected to a respective one of the connectionless information cell assembly/disassembly means 30 by an ATM network 37, for example, by a permanent virtual channel and has input and output interfaces dedicated to connectionless cells bound for two or more destinations. The routing control means 36 further includes a multiplexing section for multiplexing connectionless cells input from corresponding connectionless information cell assembly/disassembly means 30 and outputting multiplexed cells from its dedicated output interface, a copying section for copying connectionless cells bound for the means itself of the connectionless cells entered from its dedicated input interface and outputting the copied cells to the corresponding connectionless information cell assembly/disassembly means 30, and a rejecting section for rejecting connectionless cells that are output from its dedicated output interface and then input to its dedicated input interface.
The ATM network 37 connects the input and output interfaces of the routing control means 36, which are dedicated to connectionless cells bound for two or more destinations, by virtual channels in the form of a ring.
In the fourth invention, connectionless cells obtained by connectionless information cell assembly/disassembly means 30 are multiplexed by the routing control means 36, for example, the multiplexing section in the server, output from the output interface dedicated to connectionless cells bound for two or more destinations and forwarded over the virtual channel that connects the dedicated input and output interfaces of the routing control means 36 in the form of a ring within the ATM network 37.
The copying section in each server monitors cells on the ring form from virtual channel, copies connectionless cells directed to its server of the connectionless cells input from its dedicated input interface and outputs them to corresponding connectionless information cell assembly/disassembly means 30. Each server, when finding connectionless cells output from it among connectionless cells input to its dedicated input interface, rejects the cells without outputting them to the succeeding server because the cells have run around the ring form from virtual channel.
The basic block diagram of a fifth invention is the same as that in FIG. 6 illustrating the principles of the first and second inventions. However, the fifth invention, unlike the first invention, is made on the premise that the ATM network 32b can set not only a virtual channel for one-to-one communication but also a virtual channel for one-to-N (xe2x89xa72) communication. The destination""s address of connectionless information is analyzed by the routing control means 31c of FIG. 6. As a result, when the connectionless information is bound for a single destination and thus one-to-one communication is to be performed, use is made of the virtual channel for one-to-one communication from the sending-area routing control means 31c to the receiving-area routing control means 31c. When the address is a group address, the virtual channel for one-to-N communication is used.
FIG. 9 is a basic block diagram of a sixth invention. In this invention, message identifiers (MIDS) are placed in individual messages in connectionless communication, and two or more messages are sent multiplexed to one virtual channel. However, the number of message identifiers that can be assigned to one virtual channel is limited to, say, 1,024. When this limit is exceeded, a problem will arise in that the communication has to be deferred until message identifiers MID become available or messages are rejected.
The object of the sixth invention is to vary the number of virtual channels between connectionless communication servers varies according to the number of messages to be transferred, thereby preventing the rejection of messages and the delays involved in deferred communications which result from the limitation on the number of MIDs.
In FIG. 9, the operation of the connectionless information cell assembly/disassembly means 30 is exactly the same as in the first invention, i.e., the two-way conversion between LAN data and fixed-length cells.
Routing control means 38, which control routes of connectionless cells within an ATM network 39, are interconnected within the ATM network 39 by a virtual channel (synonymous with a virtual circuit) through ATM switching units, and detect the number of messages transmitted over the virtual channel to determine whether or not there is a need for addition or deletion of the virtual channel.
Switching control means 40, which are switching control means for the ATM switching units connected to the routing control means 38, are responsive to the determination by the routing control means 38 to establish and release the virtual channels among the routing control means 38.
In the sixth invention, a connectionless communication server constituting the routing control means 38 detects the number of messages transferred over a virtual channel connected to another server on the basis of the number of message identifiers MIDs. The detection is made by incrementing a message counter at the time of entry of a cell in which the previously-described BOM has been placed as a segment type and decrementing it at the time of entry of a cell in which the EOM has been placed.
Subsequently, the number of messages detected is compared with a threshold. When the threshold is exceeded, the above-described switching control means 40 increases the number of virtual channels to be established between servers. When the number of messages detected is smaller than the threshold, on the other hand, the control means 40 decreases the number of the virtual channels.
In increasing or decreasing the number of the virtual channels, the usual call setting procedure is used. Therefore, there is no need of addition of a new facility to a switching unit. Thereby, a maximum number of messages that can be simultaneously communicated between servers is made variable. Varying the number of the virtual channels may dynamically be performed during communication by using hardware or may be performed over a middle or long period of time by using software.
FIG. 10 is a basic block diagram of a seventh invention. In the seventh invention, the operations of connectionless information cell assembly/disassembly means 30 and ATM network 32 are the same as in the first invention. As is the case with the first invention, routing control means 41 is a server which controls the routes of connectionless cells. In distinction to the first invention, receive-side routing control means 41b is equipped with a number-of-messages limiting section 42 which limits the number of messages sent to the receive-side LAN 17 in FIG. 3. That is, the seventh invention solves one problem with the inter-LAN connection system in which connectionless information is formed into cells for transfer through an ATM network, that is, a problem that, if messages transferred from the ATM network to the receive-side routing control means 41b, e.g., the server are sent to the receive-side LAN as they are, they may overflow the LAN-terminal site memory.
In the seventh invention, the number-of-messages limiting section 42 is constructed from a cell storage section which stores cells corresponding to each of messages that can simultaneously arrive at the receive-side server, an MID storage FIFO which stores message identifiers MIDs equal in number to messages that can be sent simultaneously to the receive-side LAN, a distribution section which distributes the MIDs to the MID storage section when cells are stored in the cell storage section, and a readout control section which reads the MIDs from the MID storage FIFO in sequence.
When cells arrives at the receive-side server and are then stored in the cell storage section, the distribution section distributes the MIDs placed in the cells to the MID storage FIFO, the readout control section reads the stored MIDs in sequence. The cells corresponding to the read MIDs are taken from the cell storage section and then sent to the receive-side LAN, thereby limiting the number of messages to be transferred.
FIG. 11 is a basic block diagram of an eighth invention. In this figure, connectionless information cell assembly/disassembly means 30 and ATM network 32 are the same in operation as in the first invention. As is the case with the first invention, routing control means 43 controls the routing of connectionless cells. However, the means 43 is distinct from the first invention in FIG. 6 in that each of transmit-side and receive-side routing control means, for example, servers 43a and 43b is equipped with an error detecting section 44 which detects cell errors.
As described previously, upon receipt of a BOM cell, the server obtains its routing information associated with the MID. Upon receipt of the EOM cell corresponding to the BOM cell, the server releases the MID for the corresponding message.
In case where there is a failure in data of a COM cell in the intermediate portion of a message, the transmit-side server stops transmission of the remaining cells and erases the temporarily stored MID.
On the other hand, the receiving server has already received the BOM cell and waits for the arrival of the EOM cell following the COM cell or cells.
However, since a cell or cells following the COM cell that has developed an error are not transmitted from the transmit side, the receive-side server is placed in the wait state until the EOM cell is received. In this state, the receive-side server cannot release the MID stored by itself. This will lock the MID, so that another processing cannot be performed and failure recovery become difficult.
It is the object of the eighth invention to provide a technique which, when an error is detected by a transmit-side server, permits a receive-side server to release a corresponding MID.
According to the eighth invention, when transmit-side server 43a detects a data failure in an intermediate COM cell resulting from segmentation of a message in its error detecting section 44, it alerts the receive-side server 43b of that data failure.
As alerting means, a failure information communicating line which is distinct from transmission lines between the ATM switching units can be provided.
In addition, when detecting an error, the transmit-side server 43a may generate a pseudo-EOM cell and sends it onto a transfer path.
Moreover, when an error is detected on the transmit side, a pseudo-erroneous cell may be generated for transmission to the path, and the receive-side server 43b may detect the error in its error detecting section 44.
Furthermore, when an error is detected on the transmit side, information on the occurrence of the error in a COM cell may be stored and then sent over the transmission path.
As described above, various types of alerting means permit the receive-side server 43b to recognize the occurrence of an error, so that it can release a reserved MID to continue subsequent processing.
FIG. 12 is a basic block diagram of a ninth invention. In this invention, the operations of the connectionless information cell assembly/disassembly means 30 and the ATM network 32 are the same as those in FIG. 6 illustrating the principle of the first invention. As in the case of the first invention, routing control means 45 is a server which controls the routes of cells. Unlike the first invention, the means 45 is equipped with an error processing section 46 which, upon receipt of the first one of cells associated with a message, detects an error in the message header and rejects the message-associated cells following the first cell.
In the routing control means 45 of the ninth invention, the error processing section is followed by a routing section which controls the routes of cells. As is the case with the first invention, the routing section retrieves routing information for the first cell in which the BOM has been placed as a segment type and temporarily stores that routing information in association with its message identifier MID. For the following cells, or the COM or EOM cell, their routing information is retrieved by the MID value. However, when an error is detected in the first cell by the error processing section 46, routing information for that cell is not stored, that is, no correspondence table is created, thereby rejecting the succeeding COM or EOM cell.
FIG. 13 is a basic block diagram of a tenth invention. In general, connectionless information, such as LAN information, is transmitted without considering traffic at destinations. Thus, when there is a lot of traffic at the receive side, cells transmitted over the ATM network cannot be handled, which may overflow a buffer at the receive side. In order to prevent the buffer from overflowing which may occur at the congestion time of the receive side, the tenth invention aims to alert the transmit side separated from the receive side by the ATM network of the congestion condition at the receive side to thereby control the traffic from the transmit side.
In FIG. 13, buffer capacity monitoring means 47 monitors the capacity of a buffer for receiving connectionless information cells and, when, for example, xc2xe of the buffer capacity is exceeded by the cells, issues an alarm signal indicating the congestion state. Congestion informing means 48 comprises a periodic cell generating section which periodically generates a cell for alerting the transmit side of the congestion state at the receive side, and a congestion state marking section for marking connectionless information cells with alert information. Upon receipt of an alarm signal from the capacity monitoring means 47, the means 48 alerts the transmit side of the congestion state at the receive side.
The traffic control means 49 at the transmit side, which controls the transmission of cells according to the alert information from the receive side, is constructed from a transmission control signal generating section which is responsive to the alert information to generate a collision signal as a transmission control signal and send it onto a bus on the transmit side, and a carrier sense multiple access with collision detection (CSMA/CD) protocol processing section which scans information on the bus and controls the transmission of cells upon detecting a collision signal.
In FIG. 13, when xc2xe of the capacity of the buffer at the receive side is exceeded, the buffer capacity monitoring means 47 issues an alarm signal to the congestion alerting means 48. The congestion alerting means 48, which is constructed from the periodic cell generating section and the congestion state marking section, marks connectionless information cells to be transmitted to the receive side, if any, with congestion alerting information. If, on the other hand, there is no information cells to be transmitted, the cell generated by the periodic cell generating section is used for alerting the transmit side of the congestion state at the receive side. To alert the transmit side, the reserved portion in the header of a connection information cell or a periodic cell is used.
At the transmit side, the congestion information from the receiving side is received by the traffic control means 49. In the traffic control means 49 which, as described above, is constructed from a transmission control signal generating section and a CSMA/CD protocol processing section, a collision signal is sent out onto the bus at the transmit side when congestion information is received, and the collision signal is detected by the CSMA/CD protocol processing section, so that the transmission of cells is controlled.
As described above, according to the tenth invention, the receive side alerts the transmit side of its congestion state, thereby controlling the transmission of cells from the transmit side.